1. Field of the Invention
The present invention relates to an intake system of an internal combustion engine (hereinafter, the internal combustion engine being referred to as an “engine”) and, more particularly to an intake system in which a functional part is fixed to a tubular portion such as an intake pipe, a resonator for reducing noise generated by intake air flowing through an intake passageway and an intake member for supplying intake air to the engine, and a method for producing the system.
2. Description of the Related Art
Conventionally, an intake pipe of an intake system that is formed into a tubular shape is formed by joining a plurality of half hollow members which are divided at a plane extending along, for example, a central axis. In the case of the intake system, a functional part such as an airflow meter is placed in the intake pipe. The functional part is attached to the tubular portion with a fastening member such as a tapping screw or bolt. The fastening member is, however, gradually loosened as the tubular portion vibrates due to vibrations of the engine to which the intake system is attached. To cope with this, according to a technique disclosed in, for example, Japanese Unexamined Patent Publication No. 2000-257612, the loosening of two taping screws attributed to such vibrations is prevented by causing a straight line connecting the two taping screws to deviate from a central axis of an O ring.
However, not only the airflow meter but also a plurality of functional parts such as other sensors and actuators are placed on a tubular member such as the intake pipe. Due to this, as the number of functional parts increases, the number of fastening members for fixing the functional parts increases. As a result, there is caused a problem that the increase in number of components, and in the number of processes for installing fastening members, is called for. In addition, it is difficult to prevent the loosening of the functional parts attached by the fastening members over a long period of time.
In addition, conventionally, a resonator is disposed on the intake system for reducing the noise generated by intake air flowing through the intake passageway. The resonator is constructed by covering an opening in an intake duct forming the intake passageway with a casing having a predetermined volume, whereby the intake passageway is partially enlarged so as to reduce the noise generated by the flow of intake air.
In a resonator disclosed in, for example, Japanese Unexamined Patent Publication No. 8-4612, an intake duct is divided into two parts. One of the divided ducts has a resonator main body portion whose volume is enlarged in order to form a resonator. Then, the two divided intake ducts are connected together through fit, whereby a resonator is formed outside the intake duct.
In the case of the resonator disclosed in the Japanese Unexamined Patent Publication No. 8-4612, however, the resonator main body portion is formed in one of the divided intake ducts. Due to this, the intake duct and the resonator main body portion must be designed so as to match a space formed in the periphery of the engine. Namely, an intake system becomes a component dedicated to the engine used, and it is difficult to design the intake duct and the resonator main body portion separately. As a result, the degree of freedom is decreased in designing the intake system involving a change in, for example, position of the resonator relative to the intake duct.
On the other hand, it is conceivable that a separate casing is placed on the intake duct so as to form a resonator. However, in a case where a separate casing is placed on the intake duct, the casing is not supported directly by the intake duct but is fixed to the intake duct while being supported by a chassis constituting an engine compartment. This is because there is no extra space at a portion in the engine compartment where an resonator must be formed. In addition, separate members such as bands and fixtures are needed to fix the intake duct and the casing. This calls for an increase in the number of processes for assembling, and in the number of components, and a larger space is also needed to install the intake system.
Furthermore, conventionally, there has been known, as an intake member for supplying intake air to the engine, an intake member which is produced by joining a plurality of resin molded bodies. The intake member such as an intake manifold whose configuration becomes complex due to its function to distribute and supply intake air to the engine can easily be fabricated by forming respective parts thereof of resin molded bodies and thereafter joining together the respective resin molded bodies so formed.
An intake manifold is disclosed in Japanese Unexamined Patent Publication No. 10-339224 which is formed by holding an intermediate resin molded body between two outer resin molded bodies and combining and joining them together. There are known methods for fabricating such an intake manifold including a method in which an intermediate resin molded body is held between two outer resin molded bodies and these resin molded bodies are vibration welded so as to be joined all together, or a method in which an intermediate resin molded body is joined to one of outer resin molded bodies and, thereafter, the other outer resin molded body is joined to the intermediate resin molded body which has already been jointed to the one outer resin molded body.
Of the aforesaid two methods, according to the former method, in the event that an interface between the outer resin molded body and the intermediate resin molded body is situated in the interior of the intake manifold, as the transmission of welding vibration to the vicinity of the interface becomes insufficient, it is not possible to secure sufficient airtightness and joining strength. In addition, according to the latter method, as the joining of the resin molded bodies is carried out in two separate steps, problems of low productivity and high production costs occur.